The actual hardness on the inside of the fingers may be caused by warts, flat warts, dermatofibromas and other illnesses. 1. common warts: common warts is caused by human papilloma virus infection, can occur in any part of the body, but to the hands of the majority, manifested in the surface of the skin appeared hard pimples, along with the development of the disease, and gradually increase in size, increase, local friction is easy to bleed. 2. flat warts: flat warts are viral skin diseases caused by human papillomavirus infection and are commonly found on the face, hands and forearms, etc. They appear as round or oval flat papules on the surface of the skin, with a smooth surface and a hard texture, and there are no symptoms of self-consciousness, and occasionally there is a mild itching sensation. 3. Dermatofibroma: Dermatofibroma is a benign tumor caused by proliferation of fibroblasts or histiocytes, manifested as round or ovoid hard nodules on the surface of the skin, usually without conscious symptoms. There may be other causes for the hardness on the inside of the fingers, and it is recommended to go to the hospital in time to improve the examination and give targeted treatment after the cause of the disease is clear.